The Intergovernmental Panel on Climate Change released its Fourth Assessment Report in 2007. Working Group I published its full report in March 2007 after a process that took six years to complete.
Over 130 countries provided contributors for this massive undertaking with eight hundred contributing authors writing sections of the text. Four hundred fifty lead authors coordinated the final work while more than 2,500 scientific expert reviewers examined the drafts.
Carbon dioxide levels reached 379 parts per million in 2005 according to the document. Methane concentrations hit 1,774 parts per billion during the same year which far exceed pre-industrial ranges recorded over the last 650,000 years.
A paragraph in the Working Group II report projected Himalayan glaciers could disappear by 2035 but this statement appeared in chapter 10 of the original draft before being removed from the final Summary for Policymakers. The IPCC acknowledged that date as incorrect because the error originated from a misquote within a World Wildlife Fund report.
Model-based scenarios predict temperature rises between 1.8 degrees Celsius and 4.0 degrees Celsius by 2100 depending on different emission pathways chosen by human societies. A low scenario estimates a best estimate rise of 1.8 degrees with a likely range of 1.1 to 2.9 degrees while high scenarios project a best estimate increase of 4.0 degrees with a possible range up to 6.4 degrees.